Field of the Invention
The present invention relates to a process for improving the fluidity of hydrocarbon fractions and more particularly, to a process for the dewaxing of hydrocarbon fractions, typically fractions obtained from petroleum.
In recent years, kerosene, gas oil (an oil prescribed in JIS-Japanese Industrial Standard-K 2204) and A fuel oils (the first class fuel oil prescribed in JIS K 2205), which are called middle distillates, occupy an increasing proportion of the demand for petroleum with the definite tendency toward a lowering of the demand for B and C fuel oils (corresponding to the second and third class fuel oils prescribed in JIS K 2205). One of the useful methods of improving the yield of the middle distillate includes a dewaxing process in which the pour points of gas oil and A fuel oil are lowered. In general, if hydrocarbon fractions have a good or improved fluidity or pouring property at the time of storage, transportation or combustion, when used in various applications, there are obtained great benefits not only in increasing the yield of the middle distillates, but also in increasing the flexibility of the selection of crude oil in the refining of petroleum and permitting much easier handling of petroleum products in the winter.
Known dewaxing processes for improving fluidity of lubricant oils, which have been widely used, include solvent dewaxing processes typical of which is the MEK process, and the urea dewaxing process. However, these known dewaxing processes are all complicated and high in operating cost, with another disadvantage being that secondarily produced waxes (by-products) do not always have a sufficiently high added value. Accordingly, there is a demand for a new, effective dewaxing process or method.
In order to meet the demand, there has been proposed a process for lowering the pour point of hydrocarbon fractions in which zeolite catalysts are used to selectively convert and remove waxes from hydrocarbon fractions. The following three types of zeolite catalysts are known for such use.
(1) Zeolites capable of adsorbing n-paraffins but incapable of adsorbing hydrocarbons having a larger molecular diameter than iso-paraffins: See zeolite A (Canadian Pat. No. 877,293), and Elionite (U.S. Pat. No. 3,575,846).
(2) Zeolites capable of adsorbing n-paraffins and monomethyl-substituted paraffins but incapable of adsorbing hydrocarbons containing a quaternary carbon atom such as 2,2-dimethylbutane: See zeolite ZSM-5 (U.S. Pat. No. 3,700,585 and U.S. Pat. No. Re. 28,398).
(3) Zeolites capable of adsorbing hydrocarbons containing a quaternary carbon atom such as neopentane and having a pore size smaller than zeolite Y: See Mordenite (U.S. Pat. No. 3,516,925).
Because n-paraffins, which are one of the main components of wax, have a molecular diameter of about 5 Angstroms, these prior art techniques make use of zeolites having a relatively small pore diameter in order to increase the selectivity of the decomposition reaction of n-paraffins. With regard to the abovementioned three types of zeolites, it is considered suitable to have pores capable of adsorbing monomethyl-substituted paraffin. Various attempts have been made to improve catalysts based on ZSM-5 zeolite. As a result, there has been proposed the use of ZSM-23, 35 having a pore size between those of (1) and (2) (See U.S. Pat. No. 4,222,855).
However, these prior art techniques have a number of drawbacks. The catalysts used are very expensive; the catalytic activities thereof are unsatisfactory, so that undesirable high reaction temperatures are required or the catalyst life is relatively short; and recovery of the dewaxed oil is low. Accordingly, a catalyst is desired which has high catalytic activity, high selectivity and long life. As a result of intensive studies on the dewaxing of hydrocarbon fractions it has been unexpectedly found that, contrary to the teachings of U.S. Pat. No. 3,700,585, pentasil-type zeolites which have a relatively large pore size, sufficient to adsorb hydrocarbons containing a quaternary carbon atom such as 2,2-dimethylbutane, are excellent as a catalyst with high activity.
An object of the present invention is to provide a process for dewaxing of hydrocarbon fractions in an atmosphere of hydrogen and in the presence of a specific type of zeolite catalyst.
Another object of the present invention is to provide a process for dewaxing hydrocarbon fractions whereby dewaxed oil is obtained in a high yield.
A further object of the present invention is to provide a process for dewaxing hydrocarbon fractions in the presence of a zeolite catalyst of high activity whereby reaction temperatures can be maintained at a level lower than those of prior art techniques.
Other objects and further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. It should be understood, however, that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.
Pursuant to the present invention, the above objects can be achieved by using a zeolite catalyst having an X-ray diffraction pattern as shown in Table 1 and the capacity of adsorbing mesitylene (1,3,5-trimethylbenzene) in an amount not less than 1.6 wt%.
Use of the specific type of zeolite catalyst which exhibits such a specific adsorption amount of mesitylene as defined above improves the diffusion of the reactant to active sites and the desorption of the resulting reaction product from the sites. Thus, the reaction activity increases with a reduction of the secondary, side reactions of the product.
The catalyst used in the practice of the present invention yields a high recovery of dewaxed oil and exhibits high activity as will be particularly shown in the examples appearing hereinbelow. When known catalysts are used, large amounts of (1) LPG and (2) naphtha or gasoline are secondarily produced as byproducts by the dewaxing reaction. The value of these materials varies greatly, depending on the balance of supply and demand of petroleum and other factors. Accordingly, the high level of recovery of dewaxed oil contributes to increasing the economical stability of the dewaxing process. This is very advantageous from an industrial standpoint. The catalyst has such a high activity that reaction temperatures can be set at a lower level than in the case of known catalysts. Accordingly, a long-run operation becomes possible while suppressing thermal deterioration of hydrocarbon oils. The dewaxed oil thus obtained possesses good color and good stability.